The present invention relates to polymer-based electrically conducting or electroluminescent films, and more particularly, to films constructed from a class of precursor polymers that are electrochemically polymerized to form the electrically conducting film.
Polymer-based electroluminescent devices (PLEDs) have the potential for providing inexpensive alternatives to alpha-numeric displays and x-y addressable displays. PLEDs also have the potential to provide an alternative to back lighted, liquid crystal displays. A simple PLED may be constructed from an electroluminescent layer sandwiched between an electron injection electrode and a hole injection electrode. The electroluminescent layer is typically constructed by depositing a conjugated or conductive polymer on one of the electrodes. Devices based on poly(p-phenylenevinylene) (PPV), or derivatives thereof, have been demonstrated with sufficient quantum yields to be commercially attractive. More complicated devices utilize electron and hole transport layers between the above mentioned electrodes and the electroluminescent layer. The electroluminescent layer generates light when holes and electrons recombine in the layer.
The deposition and patterning of the electroluminescent layer present significant technical problems that must be overcome before economically attractive devices can be fabricated. If the conjugated polymer is soluble in a solvent, a thin film can be made by the spin-coating of a polymer solution. While spin-coated polymer films having good electro-optical properties can be obtained in this manner, the adhesion of spin-coated film to the underlying layer is often insufficient. In addition, many attractive polymers are not sufficiently soluble to be applied via spin-coating.
Spin-coating and other processes in which the entire substrate is coated, present additional problems in multi-color displays in which different xe2x80x9cpixelsxe2x80x9d must be coated with different polymers. The deposition of each layer requires a three-step procedure consisting of a masking step to protect areas that are not to be coated, the spin-coating step, and a mask removal step. In addition to the increased complexity of the masking steps, the solvents utilized with conventional masking systems are often incompatible with the polymers being deposited. Accordingly, it would be advantageous to provide a system that does not require such masking operations.
Broadly, it is the object of the present invention to provide an improved method for depositing an electrically conducting or electroluminescent film.
It is another object of the present invention to provide a method that may be utilized with materials that cannot be spin-cast.
It is further object of the present invention to provide a method that can selectively deposit such films without the use of the masking operations discussed above.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.
The present invention is a method for depositing an electrically conducting film on an electrode and the film resulting from that method. An electrically conducting film according to the present invention is deposited by immersing the electrode in a solution of a precursor polymer in a predetermined solvent. The precursor polymer includes a plurality of electrochemical polymerizable monomers. Each monomer has first and second polymer-forming active sites that can be joined by electrochemical polymerization and third and fourth polymer-forming active sites that can be joined chemically in solution. The precursor polymer is constructed from the monomers joined by the third and fourth polymer-forming active sites. The precursor polymer is soluble in the solvent whereas a polymer formed by electrochemical polymerization of the first and second polymer-forming active sites is insoluble in the solvent. An electrical potential is applied to the electrode to cause monomers of the precursor polymer molecules to be joined electrochemically by their first and second polymer-forming active sites. Precursor polymers may be constructed from monomers such as flourene, thiophene, pyrrole, biphenyl, poly(vinyl carbazole) or poly (vinyl oxy thiophene). Precursor polymers may also be constructed from dimers constructed from monomers chosen from this group. The monomers may include a spacer group bonded to one of the first or second active sites. Exemplar spacer groups include (CH2)n, (OCH2)n, or (OCH2CH2)n, where 1xe2x89xa6nxe2x89xa620. The solution may also include non-polymerized monomers or other compounds that can be electrochemically lined to the first and second polymer-forming active sites of the monomers. The concentration of the monomers by molar percent of monomeric repeat unit of polymer is between 0.01 and 99.99%. These monomeric units are joined to the first and second polymer-forming active sites of the monomers in the precursor polymers, and to each other, during the electrochemical polymerization thereby forming chains of the monomeric units that are linked to the precursor polymers by the first or second polymer-forming active sites of the monomers in the precursor polymers.